Madrid: Catalan separatists hold a mass rally Friday for independence that will kick off campaigning for a regional election billed as a de facto referendum on breaking away from Spain.

Under the slogan "Let`s start building a new country," the show of force on Catalan national day comes at a time of high political tensions in a country recovering from a bitter recession.

Polls show pro-secession candidates could win a majority of seats in the Catalan parliament in ballots on September 27 -- just three months ahead of a general election across Spain.

If they win, Catalan president Artur Mas has vowed to push through an 18-month roadmap to secession for the region of some 7.5 million people, which accounts for a fifth of Spain`s economic output.

"In your hands is the strength and the tool to mark the political future of this nation: the vote," said Mas, a conservative who is campaigning in an alliance with left-wing nationalists.

"Once the people have spoken through their vote, we will all take onboard what the majority decides," he said in a televised speech late Thursday.

Mas wants to organise an official independence referendum like those held in Scotland last year and in Canada`s French-speaking province of Quebec in 1980 and 1995, all of which resulted in a "no" to secession.

Polls show a majority of Catalans are in favour of a referendum even if they are almost evenly divided on independence.

Catalan nationalism has reached new heights during Spain`s economic downturn. Separatists say Catalonia pays an unfair level of taxes to Madrid compared to the central funding it receives.

Spanish Foreign Minister Jose Manuel Garcia-Margallo on Thursday opened the door to talks on constitutional reform and greater fiscal powers for Catalonia.Prime Minister Mariano Rajoy refuses to allow a plebiscite, arguing it violates the Spanish constitution.

"It is up to Spaniards to decide what they want Spain to be," he has repeatedly said.

On Catalan`s national day a year ago, hundreds of thousands of flag-waving separatists rallied in Barcelona. The year before, they formed a 400-kilometre (250-mile) human chain across the region.

The pro-independence list includes former FC Barcelona coach Pep Guardiola.

"We want to manage our resources ourselves," he said Tuesday, calling for "a more socially stable and prosperous country for all".

Opponents of Catalan independence are more divided.

Rajoy refuses to negotiate on independence and has not publicly discussed possible constitutional reforms.

New far-left anti-austerity party Podemos favours a referendum.

The main opposition Socialists promise a constitutional reform which would make Spain a federal state and grant Catalonia more powers.

"We should set aside the reproaches and talk about solutions," said the Socialists` leader Pedro Sanchez on Thursday.

"Both Mas and Rajoy not only lie to their people, but they hide" from the debate, Sanchez told radio station Onda Cero.

British Prime Minister David Cameron and German Chancellor Angela Merkel have backed Rajoy. Cameron has warned that Catalonia would leave the EU if it broke away from Spain.